Abstract: To improve the design level of reciprocating compressor, the VC++ and Pro/E were used to develop a system software for the fatigue reliability analysis and parametric design of piston rod. The loading state of piston rod was analyzed to find out the weak link in the design in accordance to the deformation compatibility principle of elastic mechanics and then the results were verified by FEM. A limit-state equation for the weak link was given according to the randomness of design parameters, such as geometric dimensions, machining process and material strength, so as to analyze both the reliability of fatigue strength and relevant economical level, thus determining all the design parameters of the piston rod, including dimensions, process technology and material to carry out parametric design. The results showed that the combination of reliability theory with parametric design is very promising in engineering practice.